# Seismogram (/docs/charts/seismogram)

Seismogram answers "when did things happen, and how hard?". Ticks read as a seismograph trace — centered on a midline
and flaring symmetrically: presence is density texture, length is intensity. Long series collapse via max-per-bucket
only — the spike is the chart's whole job, so it always survives, and the summary is always computed from the raw
values, never the buckets.

```tsx
import { Seismogram } from "@microcharts/react/seismogram";

<Seismogram
  data={[1, 2, 1, 3, 2, 6, 2, 1, 0, 2, 1, 4, 9, 3, 1, 2, 0, 1, 3, 2, 7, 2, 1, 0, 2, 1, 5, 11, 3, 1]}
  title="Error bursts"
/>
```

## Install

```tsx
import { Seismogram } from "@microcharts/react/seismogram";

<Seismogram data={burstsPerMinute} title="Error bursts" />
```

Setup (package + stylesheet): [Quickstart](/docs/quickstart#set-up-with-an-ai-agent) or paste [`/agent-setup.md`](/agent-setup.md) into your agent.


## When to use it

- **Good for** — error bursts per service, alert density, activity texture in rows.
- **Avoid for** — level tracking (Sparkline) or labeled events (EventTimeline).


## Variants

```tsx
// magnitudes are noise? say so — uniform ticks are presence only
<Seismogram
  data={[1, 0, 2, 1, 3, 0, 1, 2, 0, 1, 1, 0, 2, 1, 3, 1, 0, 1, 2, 1]}
  mode="barcode"
/>
```

```tsx
// negatives extend below a zero baseline (up = +, down = −)
<Seismogram
  data={[3, -1, 4, -2, 1, 5, -3, 2, -1, 4, -2, 6, -4, 1, -2, 3, -1, 2]}
  positive="up"
/>
```

```tsx
// spikes at or above the threshold flare in the alert token
<Seismogram data={burstsPerMinute} anomaly={6} />
```

```tsx
<Seismogram
  data={[3, -1, 4, -2, 12500, 5, -3, 2, -1, 4]}
  positive="up"
  format={{ maximumFractionDigits: 0 }}
  locale="de-DE"
/>
```

`format` also takes `Intl.NumberFormatOptions` — with a `locale`, the accessible summary's peak number follows that
locale's own grouping ("12.500" in German, not "12,500"). Tick positions and lengths are unaffected; only the announced
peak is localized.

## Edge cases

```tsx
// all-zero data renders the baseline at rest — never a blank hole
<Seismogram data={[0, 0, 0, 0, 0, 0]} />
```

```tsx
// series longer than the pixel width collapse via max-per-bucket ONLY,
// so a single sharp spike never gets averaged away
<Seismogram
  data={Array.from({ length: 300 }, (_, i) => (i === 210 ? 9 : i % 17 === 0 ? 2 : 0))}
/>
```


## Why this default

A centered seismograph trace over bottom-anchored bars: the symmetric flare reads as event intensity rather than
inviting the bar-to-bar magnitude comparison the strip is too small to support — and it stays visually distinct from
SparkBar. Barcode mode is documented as presence-only — a uniform tick is not intensity. `anomaly` flags spikes at or
above a threshold in the alert token; the flag is redundant with tick length, never color alone. A quiet strip renders
its baseline at rest, never a blank hole.

## Accessibility

The accessible name counts the events — **"29 events, peak 11."**, or **"No events."** for a quiet strip. The
interactive entry steps slots with position readouts ("Point 2 of 5: 3."), announces quiet slots as "no data", and
Home/End jump to the first/last event.

The interactive entry follows the shared [interaction contract](/docs/accessibility#one-interaction-contract):
arrow keys rove between units on both axes, `Home` and `End` jump to the ends, and a click, tap, `Enter` or
`Space` selects a unit — pinning its readout so it survives blur, until you select it again or press `Escape`.
On touch, a tap pins and a drag scrubs.

## Props

| Prop | Type | Description |
| --- | --- | --- |
| `data` (required) | `(number \| null)[]` | Per-slot event intensity; 0/null = quiet. |
| `mode` | `"intensity" \| "barcode"` | Barcode collapses heights — pure occurrence density. |
| `positive` | `"up" \| "down"` | Polarity coloring of signed ticks. |
| `anomaly` | `number` | Flag spikes: \|v\| ≥ threshold flares in the alert token. |
| `domain` | `[number, number]` | Fixed intensity scale across rows. |
| `animate` | `boolean` | (interactive) Opt-in entrance motion when the chart mounts client-side — add `import "@microcharts/react/motion"` once. Inert on the server, on hydrated server HTML, and under `prefers-reduced-motion`. |

Plus the shared grammar — `data`, `domain`, `color`, `title`, `summary`, `format` — and the layout props (`width`, `height`, `className`, `style`) that every chart accepts. Interactive entries also share `animate` and `live`, and — wherever a chart has more than one navigable unit — `onActive`, `onSelect`, `selectedIndex` and `defaultSelectedIndex`; and — wherever the chart shows a hover value — `readout`. See [the shared grammar](/docs/quickstart#the-shared-grammar).